- This study analyzed the association between frequency of bowel movements and incidence of diverticulitis in the Nurses' Health Study and the Health Professionals Follow-up Study
- After adjustment for other known or suspected risk factors, increased bowel movement frequency was associated with higher risk of diverticulitis in both cohorts
- Results were similar for the whole population when the data from the two cohorts were meta-analyzed
- Further research into this association could inform new targets for prevention and treatment of diverticulitis
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The conventional wisdom is that people who have more frequent bowel movements are at lower risk of asymptomatic diverticulosis. This notion has been challenged, though, by recent cross-sectional studies linking more frequent bowel movements to a higher risk of both symptomatic and asymptomatic diverticular disease. The only previous prospective study of the issue was limited to 358 hospitalized individuals with diverticulitis (published in World Journal of Gastroenterology).
Using data from two very large prospective U.S. cohorts, Andrew T. Chan, MD, MPH, director for Cancer Epidemiology in the Massachusetts General Hospital Cancer Center, chief of the Clinical and Translational Epidemiology Unit (CTEU) in the Department of Medicine and vice chief for clinical research in the Division of Gastroenterology, and colleagues determined that more frequent bowel movements do appear to be a risk factor for diverticulitis. In Clinical Gastroenterology and Hepatology they outline three potential measures for prevention and treatment.
The cohorts analyzed were:
- The Nurses' Health Study (NHS)—121,700 female nurses ages 30–55 at cohort inception in 1976; the current study included data on 58,857
- The Health Professionals Follow-up Study (HPFS)—51,529 male health professionals ages 40–75 at cohort inception in 1986; this study included data on 31,785
Both cohorts answer biennial questionnaires; in certain years participants provided information about bowel movement frequency and diagnosis of diverticulitis requiring antibiotic therapy or hospitalization.
Incidence of Diverticulitis
In the NHS, there were 5,214 new cases of diverticulitis over 24 years of follow-up (1,299,922 person-years).
In the HPFS, there were 390 new cases over 14 years (368,661 person-years of follow-up).
Baseline demographic and clinical characteristics did not differ substantially by categories of bowel movements (more than once daily, daily or less than once daily).
Influence of Bowel Movement Frequency
After adjustment for known and suspected lifestyle and dietary risk factors, the risk of diverticulitis compared with participants who reported daily bowel movements was:
- Participants with bowel movements more than once daily
- Women: HR, 1.30
- Men: HR, 1.29
- Participants with bowel movements less frequently than once daily
- Women: HR, 0.89
- Men: HR, 0.61
Results were similar for the whole population when the data from the two cohorts were meta-analyzed.
The association between bowel movement frequency and risk of diverticulitis was not modified by categories of age, dietary fiber intake, physical activity, body mass index or laxative use.
Potential Clinical Applications
These observations are biologically plausible in several ways:
- Body position while defecating is thought to influence the straightness and width of the anorectal canal, and more instances of sitting on a traditional Western commode may produce more strain and promote the formation of diverticula
- More frequent bowel movements might influence the composition of the gut microbiota, which seem to play a role in the risk of diverticulitis
- The presence of chronic low-grade inflammation may predispose to more frequent bowel movements as well as diverticulitis
These three mechanisms are not mutually exclusive; each may have a role in causing diverticulitis, which is a multifactorial disease. If the results of this study are confirmed, measures to reduce the risk of diverticulitis would include counseling patients to adopt a squatting-like or "The Thinker" position during defecation and developing therapies to beneficially alter the gut microbiota or reduce low-grade inflammation.
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